After Elizabeth Abbott got engaged to her girlfriend, she went ring-shopping at a jewelry store near her home in Minneapolis. She was caught a little off guard by a question from a saleswoman: "Can two women really get married these days?"

Still, she bought two diamond rings—one for herself and one for her fiancée. The saleswoman "was very nice, but I don't know if she'd ever met any gay people before," says Ms. Abbott, age 30, a veterans coordinator at the University of Minnesota.

The legalization of same-sex marriage in 17 states is bringing more same-sex couples into stores to buy engagement rings. Well over 70,000 legal same-sex marriages have taken place in the past decade, according to a 2013 Pew Research Center estimate based in part on state records. Jewelers—from purveyors like Tiffany & Co. and department-store chains like Macy's Inc. to smaller, specialty retailers and jewelry designers—are taking steps to woo this small but growing segment.

Before gay marriage gained ground, gay couples would typically shop together, looking for simple, gold bands, says Jeffrey Bennett, a vice president at Tiffany & Co. who runs the luxury jeweler's Manhattan flagship store.

Now, he sees an "embrace of that traditional sense of the engagement," with just one partner coming into the store, seeking more elaborate designs intended for a surprise proposal. Men, he says, are even asking for pieces with large diamonds, such as the Etoile, which has a somewhat masculine look, with diamonds set deeper into the metal.

"I can have whatever ring I want on my finger," says Douglas Marshall, a writer in New York whose fiancé gave him an emerald-cut diamond engagement ring with tapered baguettes, set in platinum, in December 2013. "My ring is nicer than some of my girlfriends' [rings]," he says.

Macy's is courting the market by participating in gay and lesbian wedding fairs, advertising in publications such as Out magazine and sponsoring gay-pride events, according to spokesman Orlando Veras.

At Signet Jewelers Ltd., whose brands include shopping-mall retailers Kay Jewelers and Jared the Galleria of Jewelry, David Bouffard, vice president of corporate affairs, wouldn't discuss outreach to same-sex couples but said the company's stores "treat all customers equally and with the same outstanding customer-service levels." Signet in February announced an agreement to acquire middle-market jeweler Zale Corp., which has about 1,680 retail locations in the U.S., Canada and Puerto Rico.

Many companies say same-sex ring buyers are such a small group they don't track it. Oliver Chen, Citigroup's specialty retail softlines and luxury analyst, says the demographic is "more symbolic than numeric."

But there is some evidence that same-sex engaged couples are more likely to purchase more rings—and more expensive rings—than male-female engaged couples. Many gay couples buy two engagement rings, one for each partner. A survey by gay and lesbian market-research firm Community Marketing Inc. and the Gay Wedding Institute of about 1,000 same-sex couples found that 66% of female and 19% of male same-sex couples purchased engagement rings. A recent study by Prudential Financial, a financial-services firm, found the median household income for gay, lesbian, bisexual and transgender families in its study was nearly 25% higher than that of the average American household.

The average price of an engagement ring in 2012 was $4,000, according to a report by the Jewelers of America group. A study by Bain & Co., a management consulting firm, showed the market for diamond engagement and wedding jewelry in 2012 was $11 billion.

Shopping for rings as a same-sex couple can be awkward. Some male couples say salespeople assume the two are a man ring-shopping with a buddy. And some female couples say jewelers think they are just friends who are browsing for fun.

Mr. Bennett of Tiffany & Co. says he tells staff to avoid blunders with same-sex customers by aiming to have "consultative dialogues." He adds, "You really need to listen and understand your customers' needs before you start making recommendations."

Some gay consumers say they prefer to shop for their engagement rings online. Google the words "gay engagement ring," and one of the top results may be the website of Mervis Diamond Importers, a family-owned jeweler that sells items online and has stores in Washington, D.C., Tysons Corner, Va., and Rockville, Md.

The jeweler began promoting a line of wedding bands aimed at same-sex couples in February 2010. Its page promoting gay wedding and engagement rings from Mervis received 301 page views when it launched in January 2010—two months before the first legal weddings took place in Washington, D.C. In January 2014, the page drew 2,665 views, according to Jonathan Mervis, who works in business development at the company. Maryland began performing same-sex marriages in January 2013.

Mervis's website home page doesn't mention gay marriage. But within its site, the company notes, "we support marriage equality and fabulous diamonds for everyone!"